1. Field of Invention
The present invention relates generally to optical network systems. More particularly, the present invention relates to modularizing functionality associated with transmitting and receiving data within optical network systems.
2. Description of the Related Art
The demand for data communication services is growing at an explosive rate. Much of the increased demand is due, at least in part, to the fact that more residential and business computer users are becoming connected to the Internet. Furthermore, the types of traffic being carried by the Internet are shifting from lower bandwidth applications towards high bandwidth applications which include voice traffic and video traffic.
To accommodate the growth and demand for Internet services, service providers are rapidly installing network switching devices, such as routers, and upgrading physical media throughout their networks. For user access, dial-in lines are being replaced by digital subscriber loop (DSL), cable modem, and broadband fixed wireless. Increasingly, the network backbone exploits optical fiber physical media. Fiber is also being deployed further toward the network edge so that, for example, data over cable networks are being transformed into hybrid fiber cable (HFC) networks. However, even with these advances in data networking technologies and the high level of investment by service providers, demand for network bandwidth continues to outpace supply.
In an effort to increase the bandwidth associated with data networking technologies, and, further, to provide improved data transmissions capabilities, the length of fibers in a network is being increased. Specifically, the length of fibers and, hence, the transmissions capabilities of optical transmissions systems, is being increased. Optical fiber transmissions systems are often connected as specified by a synchronous optical network (SONET) standard, a synchronous digital hierarchy (SDH) standard, or an optical transport network (OTN) standard. SONET establishes Optical Carrier (OC) levels, SDH establishes Synchronous Transport Module (STM) levels, and OTN establishes Optical Channel Transport Unit (OTU) levels, or bit rates at which data streams may be transmitted across an optical network. At present, the OC-48 level for SONET equipment and the STM-16 level for SDH equipment, which are associated with a 2.5 Gigabit per second (Gbps) bit rate, and the OTU-1 level which is associated-with 2.7 Gbps bit rate, are widespread, although the OC-192 and STM-64 levels for SONET and SDH equipment, respectively, which are associated with a 10.0 Gbps bit rate, and the OTU-2 level for OTN equipment, which is associated with a 10.7 Gbps bit rate, are becoming more prevalent. SONET arid SDH equipment, which may operate at a still higher speed, e.g., bit rate of 40.0 Gbps, as specified by the OC-768 and STM-256 levels, and OTN equipment, which may operate at bit rate of 43.0 Gbps, are under development.
Increasing the transmissions range over which data is transferred generally increases chromatic dispersion (CD) and polarization mode dispersion (PMD) of the fiber. As will be appreciated by those skilled in the art, CD generally occurs when each spectral component of modulated light travels at different speeds over a fiber, or a wire, thereby causing intersymbol interference (ISI). ISI caused by CD typically increases with the length of the fiber. Another effect that causes ISI is PMD. When an optical pulse excites both orthogonal polarization components within the fiber, the optical pulse becomes broader at the fiber output since the two polarization components disperse along the fiber because of their different group velocities. To characterize a PMD effect, differential group delay (DGD) is often used. As the length of a fiber increases, the DGD between two orthogonal polarization states increases, resulting the ISI.
When a system is to be upgraded from one level to another, as for example from the OC-48 level to the OC-192 level, or the range of a system is to be increased, the components and the circuitry associated with the system must often be replaced or altered. Components often must be added to compensate for increased effects of CD and PMD. Generally, the effects of CD and PMD increase as the distance over which a signal must travel increases, as previously mentioned. The effects of CD and PMD within a system also increase significantly as an associated bit rate increases, because CD and PMD effects are constant for defined fiber length, while the bit time interval decreases. Hence, changes to a system associated with a network may require substantial changes in circuitry and components used in a transceiver system which transmits and receives information on the network.
In addition to changes in components and circuitry associated with compensating for CD and PMD, network devices, e.g., line cards which include components and circuitry associated with transceivers and receivers are often of different sizes for different standards, different levels, and for different transmissions ranges, and the wiring associated with the cards often also has to be changed when an upgrade in a system is to be made. System software associated with different standards is also generally not compatible between different standards. Further, thermal requirements may also be different for different standards and levels, e.g., more heat sinks may be needed for higher bit rates or longer transmissions ranges. As a result, upgrading a system to a higher transmissions range, for example, is often a time-consuming, expensive process.
Since the demand for faster bit rates over longer ranges is ever increasing, upgrading SONET, SDH, or OTN equipment to support faster bit rates is occurring more frequently. As such, what is desired is a method and an apparatus for enabling upgrades in SONET, SDH, or OTN equipment to be made efficiently.
The present invention relates to a modularized network component system which includes a transceiver module and a separate accessory module, and enables the transmissions range of the transceiver module to be augmented, i.e., expanded, by the accessory module. According to one aspect of the present invention, an optical network includes a first device, and a second device. The first and second devices are coupled to a fiber such that the second device is in communication with the first device through the fiber. The second device includes a first modular subsystem that is arranged both to transmit data and to receive data through the fiber, as well as to process optical data and electrical data. The first modular subsystem is substantially physically decoupleable from the second device and from the fiber such that the first modular subsystem may be readily replaced within the second device by another modular subsystem.
In one embodiment, the first modular subsystem includes a transceiver module that supports a short reach transmissions range. In such an embodiment, the first modular subsystem may also include an accessory module that augments the transmissions range supported by the transceiver module. The accessory module is arranged to cooperate with the transceiver module to improve the transmissions range of the transceiver module.
The use of a transceiver module that may be decoupled from a line card or similar device enables the performance of the line card to be readily changed, e.g., improved. Further, the use of accessory modules to expand upon the transmissions range of the transceiver module enables functionality to effectively be added to the transceiver module without requiring that the transceiver module be modified. In general, the use of modules which are substantially independent of a host device enables the modules to be upgraded without requiring that the host device be substantially modified. Hence, using a transceiver module and an accessory module provides a relatively low cost, effective method for upgrading the performance of a network device on a network, e.g., from an OC-48, an STM-16 and an OTU-1 level to an OC-192, an STM-64, and an OTU-2 level, respectively, or from the OC-192 level, the STM-64 level, and the OTU-2 level to an OC-768 level, an STM-256 level, and an OTU-3 level, respectively.
In accordance with still another aspect of the present invention, a device that is suitable for use as a part of a network that includes at least one transmission fiber has a body and a first module. The body includes a first connector part that is configured to interface with a second connector part that is a part of the first module. The first module is decoupleable from the body, and includes a receiver and a transmitter. A first connection of the first module may be coupled with the transmission fiber. When the first module is coupled to the body through the first connector part and the second connector part, the first module is arranged to communicate, e.g., exchange information, with the body.
In one embodiment, the first module is arranged to support a first transmissions range, and the device further includes a second module that is arranged to augment the first transmissions range, and is decoupleable from the body. The second module may interface with the first module through the body. In such an embodiment, the second module is arranged to augment the first transmissions range to support a second transmissions range that is substantially larger than the first transmissions range.
According to yet another aspect of the present invention, a device that is suitable for use on a network includes a body, a transceiver module, and an accessory module. The transceiver module is arranged to be removably coupled to the body, and to transmit and to receive data through the network. The transceiver module also transmits and receives data through the body, while supporting relatively short range transmissions. The accessory module is arranged to be removably coupled to the body, and also transmits and receives data through both the network and the transceiver module. The accessory module cooperates with the transceiver module to support intermediate or long range transmissions.